As fluoropolymers having functional groups, functional group-containing fluoropolymers are known which are used for fluorinated ion exchange membranes, curable fluorinated resin coating materials, etc. However, they are all basically straight chained polymers, and they are obtainable by copolymerization of a fluoroolefin represented by tetrafluoroethylene with a monomer having a functional group.
Further, a polymer containing functional groups and having a fluorinated alicyclic structure in its main chain, is also known. As a method for introducing functional groups to the polymer having a fluorinated alicyclic structure in its main chain, a method of utilizing terminal groups of a polymer obtained by polymerization, a method of subjecting a polymer to high temperature treatment to oxidize and decompose side chains or terminals of the polymer to form functional groups, or a method of copolymerizing a monomer having a functional group, and if necessary, adding treatment such as hydrolysis, to introduce functional groups, is, for example, known (see Patent Documents 1, to 4).
The above-mentioned methods are available as methods for introducing functional groups to a polymer having a fluorinated alicyclic structure in its main chain. However, the method for introducing functional groups by treating the terminal groups of the polymer, has a drawback that the functional group concentration is low, and no adequate characteristics of the functional groups can be obtained. Whereas, by the method for introducing functional groups by copolymerizing a monomer having a functional group, there will be a problem such that if the functional group concentration is increased, the mechanical properties tend to deteriorate due to a decrease of the glass transition temperature (Tg).
A resist material utilizing an acid catalytic reaction in a reaction mechanism, such as a chemical amplification resist, is patterned through a process of e.g. formation of a resist coating film, exposure, baking after the exposure and development. It is known that, during the patterning, an acid produced by irradiation of active chemical rays is deactivated by a reaction with a compound reactive with an acid, such as an amine floating in the air as an impurity, whereby formation of a resist image is hindered or a change in sensitivity occurs. Such a problem is described in e.g. Non-Patent Document 1. To be left between the exposure and the baking after exposure, presents a substantial adverse effect to the properties of the resist. Namely, a PED effect (Post Exposure Delay effect) is well known, wherein the resist sensitivity abruptly decreases and thus no pattern formation tends to be formed in a case of prolongation of the time to be left between the exposure and the baking after exposure.
As one of methods to lower the PED effect, a method is known wherein a polymer film (resist protective film) not compatible with a resist film is formed on the resist film, as disclosed in e.g. Patent Document 5. This method is a method for forming the resist protective film to prevent an amine or the like floating in the air from entering into the resist film. Such a method has a drawback that the number of process steps increases by the steps for formation and removal of the resist protective film.
Further, in order not to impair the properties of the resist material, it is necessary that the resist protective film be “transparent” to radiation such as X-rays or ultraviolet rays to be used in the resist process. Namely, the composition for a resist protective film is also required not to absorb radiation such as X-rays or ultraviolet rays and not to undergo a side reaction such as insolubilization. However, most of materials to be used for the composition for a resist protective film which are considered to have an effect of suppressing the PED effect, fail to satisfy the above conditions.
Particularly for ArF excimer laser (193 nm) or F2 excimer laser (157 nm), no compositions for a resist protective film have heretofore been found, which have both transparency and an effect of sufficiently suppressing the PED effect.
On the other hand, by the liquid immersion exposure technique, exposure at high resolution will be possible by employing a liquid having a high refractive index between a lens and a resist film, but there are problems such that the resist film swells, and impurities produced from the resist film are dissolved in an upper portion of the liquid thereby causing contamination of the lens.
As one of the methods to solve such problems, it is desired to employ a method wherein a resist film is coated with a composition for a resist protective film not compatible with both the liquid having a high refractive index and the resist film, and further capable of lowering the PED effect as mentioned above.
For example, Patent Document 6 discloses that a cyclic or linear perfluoroalkyl polyether is effective as a material for forming a resist protective film. However, there are no disclosure about lowering of the PED effect, and a perfluoroorganic compound is used to remove the resist protective film, which makes the process cumbersome.
Patent Document 1: JP-A-4-189880
Patent Document 2: JP-A-4-226177
Patent Document 3: JP-A-6-220232
Patent Document 4: WO02/064648
Patent Document 5: JP-A-4-204848
Patent Document 6: WO04/074937
Non-Patent Document 1: S. A. MacDonald et al., Proc. SPIE, Vol. 1466, P2(1991)